I 

ife 

-   DEC 


The  Sulfonation  of  Benzene 


BY 
ADELBERT  WILLIAM  HARVEY 


f 


A  DISSERTATION 


PRESENTED  TO  THE  FACULTY  OF  THE  GRADUATE  SCHOOL  OF  THE 

UNIVERSITY  OF  PITTSBURGH  IN  PARTIAL  FULFILMENT  OF  THE 

REQUIREMENTS  FOR  CANDIDACY  FOR  THE  DEGREE 

OF   DOCTOR   OF   PHILOSOPHY 


PITTSBURGH,  PENNSYLVANIA 

J922 


The  Sulfonation  of  Benzene 


BY 
ADELBERT  WILLIAM  HARVEY 


A  DISSERTATION 

PRESENTED  TO  THE  FACULTY  OF  THE  GRADUATE  SCHOOL/  OF  THE 

UNIVERSITY  OF  PITTSBURGH  IN  PARTIAL  FULFILMENT  OF  THE 

REQUIREMENTS  FOR  CANDIDACY  FOR  THE  DEGREE 

OF   DOCTOR   OF   PHILOSOPHY 


PITTSBURGH,  PENNSYLVANIA 
J922 


ACKNOWLEDGMENT 

The  author  wishes  to  express  his  appreciation  of  the  kind 
assistance  given  by  Dr.  Gebhard  Stegeman,  under  whose 
direction  this  investigation  was  carried  out. 


6  ;)">()  7 


The    Sulfonation  of  Benzene 


The  action  of  sal/uric  acid  on  benzene  has  interested  a  number 
of  investigators,  principally  because  of  the  importance  of  the  resulting 
product  in  the  manufacture  of  picric  acid  during  the  war. 

The  authors  were  interested  in  a  study  of  the  sulfonation  of  ben- 
zene resulting  from  the  passage  of  vaporized  benzene  through  sul- 
furic  acid,  with  the  view  toward  finding  the  best  conditions  which 
would  increase  the  efficiency  of  the  sulfonation  and  reduce  the  possi- 
bility of  certain  undesirable  side  reactions  to  a  minimum. 

AN  EXCELLENT  paper  by  Peterkin1  gives  an  idea  of 
the  various  methods  that  have  been  devised  for  the 
production  of  benzene  monosulfonic  acid.  The  princi- 
pal difficulty  encountered  in  the  process  of  refluxing  benzene 
with  sulfuric  acid  at  about  100°  to  110°  C.  is  that  a  large 
part  of  the  sulfuric  acid  is  never  converted  into  the  sulfonic 
acid,  because  the  reaction  reaches  an  equilibrium  when  the 
sulfuric  acid  decreases  to  a  concentration  of  78  per  cent  calcu- 
lated on  the  basis  of  the  water  present.  The  loss  of  acid  and 
the  necessity  for  its  removal  before  using  the  sulfonic  acid 
produced  in  subsequent  operations  have  furnished  the  occasion 
for  a  study  of  conditions  leading  to  a  more  complete  utiliza- 
tion of  the  original  sulfuric  acid. 

MATERIALS 

The  benzene  was  repeatedly  washed  with  concentrated 
sulfuric  acid  and  the  treatment  was  continued  until  no  color 
could  be  observed  in  the  acid  layer.  After  neutralization  of 
the  acid  in  the  benzene  with  a  dilute  solution  of  alkali  and 
separation  of  the  hydrocarbon  layer,  the  benzene  was  dis- 
tilled. The  fraction  boiling  between  79°  and  82°  C.  was 
collected,  dried  over  metallic  sodium,  and  redistilled,  the 
final  product  having  a  practically  constant  boiling  point. 

The  sulfuric  acid  was  of  the  ordinary  C.  P.  variety,  free 
from  metallic  salts,  such  as  calcium,  iron,  and  manganese, 
which  might  exert  a  catalytic  effect.  Analysis  showed  it  to 
be  93.20  per  cent  sulfuric  acid. 

EXPERIMENTAL  PROCEDURE 

Fig.  1  illustrates  the  method  employed  for  the  sulfonation. 
The  benzene  was  vaporized  in  the  flask,  A.  The  flask  was 

i  Ind.  Eng.  Chem.,  10,  738  (1918). 


heated  by  a  water  bath  placed  upon  an  electric  heater, 
whereby  the  flow  of  benzene  vapor  was  made  as  uniform  as 
possible.  S  is  the  sulfonation  chamber  containing  the  sul- 
furic  acid.  An  outer  jacket,  0,  containing  a  solution  of 
glycerol  in  water,  boiling  at  the  temperature  desired  for  the 
sulfonation,  served  to  control  the  temperature.  The  tube 
conducting  the  vapors  of  benzene  into  the  acid  terminated  in 
a  bulb  having  several  holes  of  small  diameter.  A  large  num- 
ber of  small  bubbles  of  benzene  vapor  were  thus  produced  with 
a  relatively  large  surface  for  contact  with  the  acid.  The 
rest  of  the  apparatus  is  self  explanatory. 

The  glycerol-water  solution  in  the  outer  jacket  was 
heated  to  the  desired  temperature  of  sulfonation,  after 
which  the  vapor  of  benzene  was  forced  through  the 
sulfuric  acid  contained  in  the  inner  jacket.  The  original 
quantity  of  acid  was  50  cc.  To  permit  the  maximum 
amount  of  action  and  to  minimize  temperature  changes,  the 


FIG.  1 


flow  of  vapor  was  so  adjusted  that  relatively  little  change  in 
temperature  was  noticeable,  and  so  that  sufficient  benzene 
vapor  would  escape  from  the  acid  and  thus  carry  away  the 
water  formed  in  the  reaction.  By  this  procedure  the  acid 
was  prevented  from  becoming  too  dilute  to  react  with  the 
benzene.  The  results  obtained  indicate  that  in  this  way  prac- 
tically all  the  acid  becomes  available  for  sulfonation. 
Samples  were  removed  from  the  reaction  chamber  at  regu- 
lar intervals  and  analyzed  to  determine  the  progress  of  the 
reaction. 


ANALYSIS  OF  REACTION  PRODUCTS 

SULFURIC  ACID — Sulfuric  acid  was  estimated  as  barium 
sulfate.  The  required  sample  was  diluted  with  distilled 
water,  insoluble  substances  were  filtered  off,  and  the  acid 
precipitated  as  barium  sulfate.  The  addition  of  some  picric 
acid  to  the  solution  aids  materially  in  the  production  of  a 
coarse-grained  precipitate. 

BENZENE  MONOSULFONIC  ACID — The  monosulfonic  acid 
was  estimated  indirectly.  The  total  acidity  was  measured 
by  means  of  0.1  N  sodium  carbonate  solution,  using  methyl 
orange  as  indicator.  The  sulfuric  acid  present  having  been 
estimated  as  mentioned,  the  monosulfonic  acid  was  estimated 
by  difference. 

DIPHENYL  SULFONE — On  account  of  the  appreciable  solu- 
bility of  diphenylsulfone  in  water,  the  following  method 
was  employed  to  estimate  the  quantity  of  this  product.  The 
sample  was  diluted  with  200  cc.  of  water  and  neutralized 
with  dry  sodium  carbonate,  as  light  excess  being  used.  The 
solution  was  then  evaporated  to  dryness  and  heated  at  110° 
C.  for  several  hours.  The  residue  was  next  extracted  with 
petroleum  ether  in  a  Soxhlet  extraction  thimble  which  had 
previously  been  treated  with  this  same  solvent  to  remove  all 
soluble  material.  Twelve  to  fourteen  hours  of  extraction 
were  necessary  to  remove  all  the  sulfone,  but  the  results 
were  completely  satisfactory. 


FIG.  2 

UNSULFONATED  BENZENE — The  amount  of  unsulfonated 
benzene  was  found  to  be  so  small  that  it  was  not  esti- 
mated. 

WATER — For  reasons  mentioned  later  it  was  necessary  to 
estimate  the  water  content  of  the  samples  directly.  The 
usual  method,  calculating  this  quantity  by  difference,  was 
not  applicable  on  account  of  the  small  amount  present  in 
some  samples  and  because  a  certain  quantity  of  charred 
products  was  always  present,  being  formed  especially  at 
the  higher  temperatures.  The  calculation  was,  therefore, 


9 

too  inaccurate  to  have  any  significance.  The  apparatus 
shown  in  Fig.  2  illustrates  the  method  employed  in  the  esti- 
mation of  the  water  content  of  the  samples.  A  represents  a 
carbon  dioxide  generator,  the  gas  from  which  was  dried  by 
passage  through  the  large  tube,  B,  filled  with  calcium  chloride. 
The  gas  then  passed  through  the  reaction  chamber,  C  (a 
4  X  20-cm.  test  tube),  and  out  through  the  calcium  chlo- 
ride absorption  tubes,  D  and  E,  and  the  protector  tube, 
F.  A  weighed  sample  of  the  reaction  products  was  placed 
in  C,  a  known  weight  of  distilled  water  added  from  a 
Lunge  pipet,  and  the  acid  solution  formed  neutralized  with 
an  excess  of  anhydrous  sodium  carbonate  which  had  been 
dried  for  several  days  at  180°  C.  The  temperature  of  the 
oil  bath  surrounding  C  was  then  gradually  raised  to  180°  C., 
while  a  stream  of  carbon  dioxide  was  passed  through  the 
apparatus.  The  water  collected  in  the  absorption  tubes, 
D  and  E,  included  the  amount  present  in  the  sample,  the 
amount  added  from  the  pipet,  and  that  formed  in  the  neu- 
tralization of  the  acids  present.  The  concentration  of  the 
acids  in  the  sample  and  also  the  amount  of  water  added 
being  known,  the  total  amount  of  water  originally  present 
was  obtained  by  difference. 

.  RESULTS 

The  results  obtained  are  shown  in  Figs.  3  to  7  and  in 
Table  I.  , 

TABLE  I 

Temperature  H2SO4           H2O  H2SO4  Mean 

0  C.               Sample  Per  cent  Per  cent  H2SO4  +  H2O       Value 

130                     3  13.15           3.85  0.775  0.7753 

4  8.06           2.30  0.778 

5  6.20            1.82  0.773 

140         3  15.60  3.60  0.769      0.7700 

4  5.13  1.52  0.771 

150         1  12.74  3.92  0.765      0.7647 

2  6.92  2.14  0.764 

3  4.60  1.40  0.765 

160         2        9.50     3.00       0.760      0.7590 

3        6.26     2.01       0.758 
170         1        8.57     2.91       0.746      0.746 

DISCUSSION  OF  RESULTS 

The  concentration  of  sulfuric  acid  decreases  rapidly  at 
first,  and  then  more  slowly  as  the  sulfonation  proceeds.  A 
value  is  eventually  reached  below  which  the  concentration 
does  not  seem  to  fall.  This  is  probably  due  to  the  regenera- 
tion of  sulfuric  acid,  which  is  formed  by  the  decomposition  of 
the  monosulfonic  acid  into  sulfuric  acid  and  diphenylsulfone. 
This  is  particularly  noticeable  at  170°  C.,  where  the  sulfuric 
acid  concentration  becomes  constant  in  the  neighborhood  of 
0.60  per  cent. 

The  concentration  of  the  monosulfonic  acid  increases  rap- 
idly at  first,  then  more  slowly  as  the  reaction  proceeds,  the 
rate  being  greater  at  the  higher  temperatures.  The  concen- 
tration reaches  a  maximum  and  then  decreases,  owing  to  the 
formation  of  diphenylsulfone.  The  maximum  concentra- 


10 


OOf 


11 


, 

2- 


\ 


5. 


X 


2% 


13 

tion  appears  to  be  between  88  and  92  per  cent,  depending  on 
the  temperature. 

The  formation  of  diphenylsulf one,  though  not  very  evident 
at  the  lower  temperatures,  follows  the  same  general  course  as 
at  the  higher  temperatures.  The  sulfone  makes  its  appear- 
ance shortly  before  the  limiting  value  of  the  monosulfonic 
acid  is  reached.  In  every  case  the  concentration  of  the 
sulfuric  acid  has  fallen  to  10  per  cent  or  lower.  The  forma- 
tion, of  the  sulfone  may  be  ascribed  to  three  possible  reac- 
tions: 

2C6H5S08H  — >  (C6H6)2S02  +  H2SO4  (1) 

2C6H6  +  H2S04  — >  (C6H6)2S02  +  2H2O  (2) 

C6H6SO,H  +  C6H6  — >-  (C6H6)2S02  +  H2O  (3) 

The  first  reaction  would  account  best  for  the  apparently 
constant  limiting  value  which  the  sulfuric  acid  attains,  as 
indicated  before.  The  acid  formed  would  in  turn  be  used  in 
the  production  of  more  monosulfonic  acid  with  subsequent 
decomposition,  resulting  finally  in  the  practically  complete 
decomposition  of  all  the  monosulfonic  acid  into  diphenyl 
sulfone. 

The  second  reaction  is  more  likely  to  occur  when  the  sul- 
furic acid  concentration  is  high,  but  the  results  indicate  that 
very  little,  if  any,  sulfone  is  produced  in  the  early  stages  of 
the  sulfonation,  so  that,  unless  the  sulfuric  acid  present  at 
this  stage  would  serve  to  reverse  the  reaction  indicated  in  the 
first  equation,  which  does  not  appear  likely,  it  seems  logical 
to  exclude  this  reaction  as  a  cause  of  the  formation  of  the 
sulfone. 

The  third  reaction  has  generally  been  accepted2  as  the 
chief  cause  of  the  formation  of  the  sulfone,  but  it  does  not 
account  for  the  final  uniform  concentration  of  sulfuric  acid 
found  in  the  sulfonation  samples.  It  appears  logical,  there- 
fore, to  assign  the  formation  of  the  sulfone  to  a  combination 
of  the  first  and  third  reactions. 

It  has  been  previously  mentioned  that  in  the  older  process 
of  heating  benzene  and  sulfuric  acid  together  the  reaction 

TT    Of"\ 

came  to  an  equilibrium  when  the  ratio  H  SQ2  ,  4H  Q  became 

0.78.  In  the  samples  analyzed  one  of  the  quantities  that  was 
estimated  was  the  water  content,  provided  it  was  present  in 
sufficient  quantity  to  make  an  estimation  possible.  Table  I 

TT    Of) 

gives  the  ratio  TT  0~ 2  .  4TT  *•  and  the  results  obtained  indicate 
HzoO4  +  H2O 

that  this  ratio  suffers  little  change  as  the  sulfonation  proceeds, 
even  a  change  in  temperature  from  130°  to  170°  C.  reducing 
the  ratio  only  from  0.773  to  0.746.  It  is  obvious,  therefore, 
that  the  process  consists  in  simply  removing. the  water  formed 
in  the  reaction,  thus  making  more  sulfuric  acid  available  for 
sulfonation.  In  this  manner  practically  all  the  original  sul- 
furic acid  may  be  converted  into  monosulfonic  acid,  and  if  the 
reaction  is  not  continued  too  long  the  formation  of  diphenyl 
sulfone  will  be  negligible. 

2  Guyot,  Chimie  &•  Industrie,  2,  879  (1919). 


14 

From  the  standpoint  of  time  consumed  and  energy  required 
to  vaporize  the  benzene  used,  the  process  can  best  be  carried 
out  at  160°  to  170°  C.  At  this  temperature  the  formation  of 
diphenyl  sulfone  is  no  more  noticeable  than  at  the  lower 
temperatures,  as  in  all  cases  only  traces  of  the  sulfone  were 
observed  while  the  concentration  of  the  sulfonic  acid  was  rising 
to  its  well-defined  maximum.  The  higher  temperature  might 
appear  to  be  ideal  for  the  formation  of  a  black  charred  residue 
so  often  found  in  organic  reactions,  but  even  this  is  scarcely 
more  noticeable  than  at  the  lower  temperatures  at  which 
observations  were  made.  The  quantity  of  charred  products 
rarelv  exceeded  2  or  3  per  cent  of  the  total  reaction  product. 


BIBLIOGRAPHY 

F.  Thummler,  Ger.  214,156. 
H.  Sasa,  Jap.  34,824. 
A.  Heineman,  Brit.  12,260. 
C.  Ellis,  U.  S.  1,191,880. 

C.  R.  Downs,  U.  S.  1,321,994. 

D.  Tyrer,  U.  S.  1,210,725;  Brit.  103,204. 

R.  Behrend  and  M.  Mertelsman,  Ann.,  378,  352-65. 
C.  R.  Downs,  U.  S.  1,279,295. 
C.  R.  Downs,  U.  S.  1,301,785. 
A.  Bender,  U.  S.  1,301,360. 

J.  A.  Ambler  and  H.  D.  Gibbs,  U.  S.  1,300,227;  U.  S.  1,300,228. 
F.  C.  Button,  Brit.  147,967. 
L.  M.  Dennis,  Brit.  109,709. 
Barret  Company,  Brit.  122,169. 
H.  Bull,  U.  S.  1,247,499. 

A.  G.  Peterkin,  Jour.  Ind.  &  Eng.  Chem.,  10,  738-44  (1918). 
A.  Guyot,  Chimie  &  Industrie,  2,  879  (1919). 

J.  A.  Ambler  and  W.  J.  Cotton,  Jour.  Ind.  &•  Eng.  Chem.,  12,  968-9 
(1920). 


VITA 

Adelbert  William  Harvey  was  born  in  Central  Square, 
New  York,  March  8,  1894.  His  elementary  and  high  school 
training  were  received  there.  After  teaching  one  year  in 
public  school,  he  entered  Colgate  University  and  at  the 
end  of  the  Freshman  Year  transferred  to  Syracuse  University. 
He  was  graduated  in  1917  with  the  degree  of  Bachelor  of 
Science  in  Chemistry.  He  took  up  graduate  work  at  the 
University  of  Pittsburgh  in  September,  1917,  and  received 
the  degree  of  Master  of  Science  in  1919.  During  this  time 
and  while  continuing  his  studies  toward  the  degree  of  Doctor 
of  Philosophy,  he  served  as  instructor  in  inorganic  chemistry. 


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